diff --git a/Source/LibationAvalonia/ViewModels/MainVM.BackupCounts.cs b/Source/LibationAvalonia/ViewModels/MainVM.BackupCounts.cs
index ea34788b..c2a76350 100644
--- a/Source/LibationAvalonia/ViewModels/MainVM.BackupCounts.cs
+++ b/Source/LibationAvalonia/ViewModels/MainVM.BackupCounts.cs
@@ -1,4 +1,5 @@
 using ApplicationServices;
+using Avalonia.Threading;
 using DataLayer;
 using LibationFileManager;
 using ReactiveUI;
@@ -77,6 +78,9 @@ partial class MainVM
 
 		if (Configuration.Instance.AutoDownloadEpisodes
 			&& stats.PendingBooks + stats.pdfsNotDownloaded > 0)
-			await BackupAllBooksAsync(stats.LibraryBooks);
+		{
+			// RunWorkerCompleted has no SynchronizationContext; queue items require the UI thread.
+			await Dispatcher.UIThread.InvokeAsync(async () => await BackupAllBooksAsync(stats.LibraryBooks));
+		}
 	}
 }
diff --git a/Source/LibationUiBase/ProcessQueue/ProcessQueueViewModel.cs b/Source/LibationUiBase/ProcessQueue/ProcessQueueViewModel.cs
index b727bae8..9fc2ac83 100644
--- a/Source/LibationUiBase/ProcessQueue/ProcessQueueViewModel.cs
+++ b/Source/LibationUiBase/ProcessQueue/ProcessQueueViewModel.cs
@@ -255,7 +255,16 @@ public class ProcessQueueViewModel : ReactiveObject
 		&& entry.Status is ProcessBookStatus.Completed
 		&& Queue.RemoveCompleted(entry);
 
+	/// <summary>
+	/// ProcessBookViewModel requires a captured UI SynchronizationContext. Callers may resume on a
+	/// thread-pool thread after await (e.g. auto-download after BackgroundWorker).
+	/// </summary>
+	private void RunOnQueueUiThread(Action action) => Invoke(action);
+
 	private void AddDownloadPdf(IList<LibraryBook> entries, Configuration config)
+		=> RunOnQueueUiThread(() => addDownloadPdfCore(entries, config));
+
+	private void addDownloadPdfCore(IList<LibraryBook> entries, Configuration config)
 	{
 		var procs = entries.Where(e => !IsBookInQueue(e)).Select(Create).ToArray();
 		Serilog.Log.Logger.Information("Queueing {count} books for PDF-only download", procs.Length);
@@ -266,6 +275,9 @@ public class ProcessQueueViewModel : ReactiveObject
 	}
 
 	private void AddDownloadDecrypt(IList<LibraryBook> entries, Configuration config)
+		=> RunOnQueueUiThread(() => addDownloadDecryptCore(entries, config));
+
+	private void addDownloadDecryptCore(IList<LibraryBook> entries, Configuration config)
 	{
 		var procs = entries.Where(e => !IsBookInQueue(e)).Select(Create).ToArray();
 		Serilog.Log.Logger.Information("Queueing {count} books ofr download/decrypt", procs.Length);
@@ -276,6 +288,9 @@ public class ProcessQueueViewModel : ReactiveObject
 	}
 
 	private void AddConvertMp3(IList<LibraryBook> entries, Configuration config)
+		=> RunOnQueueUiThread(() => addConvertMp3Core(entries, config));
+
+	private void addConvertMp3Core(IList<LibraryBook> entries, Configuration config)
 	{
 		var procs = entries.Where(e => !IsBookInQueue(e)).Select(Create).ToArray();
 		Serilog.Log.Logger.Information("Queueing {count} books for mp3 conversion", procs.Length);
diff --git a/Source/LibationWinForms/Form1._NonUI.cs b/Source/LibationWinForms/Form1._NonUI.cs
index e8e623c5..a5708735 100644
--- a/Source/LibationWinForms/Form1._NonUI.cs
+++ b/Source/LibationWinForms/Form1._NonUI.cs
@@ -1,5 +1,6 @@
 using ApplicationServices;
 using AudibleUtilities;
+using Dinah.Core.Threading;
 using Dinah.Core.WindowsDesktop.Drawing;
 using FileManager;
 using LibationFileManager;
@@ -26,14 +27,19 @@ public partial class Form1
 
 		// wire-up event to automatically download after scan.
 		// winforms only. this should NOT be allowed in cli
-		updateCountsBw.RunWorkerCompleted += async (object? sender, System.ComponentModel.RunWorkerCompletedEventArgs e) =>
-		{
-			if (!Configuration.Instance.AutoDownloadEpisodes || e.Result is not LibraryCommands.LibraryStats libraryStats)
-				return;
+		updateCountsBw.RunWorkerCompleted += (_, e) => tryAutoDownloadAfterCounts(e);
+	}
 
-			if ((libraryStats.PendingBooks + libraryStats.pdfsNotDownloaded) > 0)
-				await BackupAllBooksAsync(libraryStats.LibraryBooks);
-		};
+	private void tryAutoDownloadAfterCounts(System.ComponentModel.RunWorkerCompletedEventArgs e)
+	{
+		if (!Configuration.Instance.AutoDownloadEpisodes || e.Result is not LibraryCommands.LibraryStats libraryStats)
+			return;
+
+		if (libraryStats.PendingBooks + libraryStats.pdfsNotDownloaded <= 0)
+			return;
+
+		// RunWorkerCompleted has no SynchronizationContext; queue items require the UI thread.
+		this.UIThreadAsync(() => _ = BackupAllBooksAsync(libraryStats.LibraryBooks));
 	}
 
 	private static object? LoadResourceImage(string resourceName)